Bulk-phase viscoelastic properties of seawater relationship with plankton components

The viscous and elastic moduli at different shear rates, togetherwith various biological oceanographic properties, were determinedin seawater from different hydrological layers in the southernNorth Sea in June. The biological oceanographic parameters includedPhaeocystis and Noctiluca abundances, chlorophyll a level (Chl),bacteria. HNAN and aggregate volume fraction. The plankton wasjointly dominated by Phaeocyslis sp. and Noctiluca scinullans.Noctiluca abundance showed no correlation with any other biologicalor viscoelastic parameter, but Phaeocystis abundance correlatedstrongly. The other biological parameters correlated with Phaeocystisand with each other positively and mostly significantly. Overall,viscoelasticity correlated more strongly with Chl than withany other biological parameter. For non-microlayer samples,the excess complex (viscoelastic) modulus (µ.Pa) G^*_E =2.0 x Ch1^1–3 (Chl in mg m^–3). Viscous and elasticmoduli also correlated closely with each other. For a givenvalue of Chl. the microlayer samples were 6.5 or 14 times (dependingon the estimation method) more viscoelastic than in bulk-phasesamples. Viscoelasticity in samples of settled benthic ‘fluff’were lower even than bulk-phase samples, but this differencewas not significant. Comparison with Mediterranean data on viscoelasticity(Jenkinson. Oceanol. Acta, 16, 317–334, 1993), using publishedvalues for phytoplankton biomass (Wiadnyana, J. Rech. Océanogr.,17, 1–6, 1992), suggests that the relationship betweenChl (or phytoplankton biomass) and viscoelasticity might begeneral. This apparent biomodification of the viscosity andelasticity of seawater is discussed in relation to its likelyimpact on turbulence and plankton ecology.     

Comparison of Lactobacillus strains with respect to bile salt hydrolase activity, colonization of the gastrointestinal tract, and growth rate of the murine host.

The significance of bile salt hydrolase production by lactobacilli in the microecology of the murine intestinal tract has not been extensively studied previously. Assays of bile salt hydrolase (sodium taurocholate as substrate) associated with cell extracts of five Lactobacillus strains of murine origin gave a range of activities (from 915 nmol of cholate released per mg of protein per 30 min to none detected). All of the strains tested colonized the murine gastrointestinal tract equally well. The growth rates of mice were not affected by colonization of their intestinal tracts by lactobacilli whether or not the bacteria produced bile salt hydrolase.     

Cloning and expression of Candida albicans ADE2 and proteinase genes on a replicative plasmid in C. albicans and in Saccharomyces cerevisiae.

Summary A plasmid vector (denoted pRC2312) was constructed, which replicates autonomously in Escherichia coli, Saccharomyces cerevisiae and Candida albicans. It contains LEU2, URA3 and an autonomously replicating sequence (ARS) from C. albicans for selection and replication in yeasts, and bla (ampicillin resistance) and ori for selection and replication in E. coli. S. cerevisiae AH22 (Leu^–) was transformed by pRC2312 to Leu^– at a frequency of 1.41 × 10⁵ colonies per g DNA. Transformation of C. albicans SGY-243 (Ura-) to Ura⁺ with pRC2312 resulted in smaller transformant colonies at a frequency of 5.42 × 10³ per g DNA where the plasmid replicated autonomously in transformed cells, and larger transformant colonies at a frequency of 32 per g DNA, in which plasmid integrated into the genome. Plasmid copy number in yeasts was determined by a DNA hybridization method and was estimated to be 15±3 per haploid genome in S. cerevisiae and 2–3 per genome in C. albicans replicative transformants. Multiple tandem integration occurred in integrative transformants and copy number of the integrated sequence was estimated to be 7–12 per diploid genome. The C. albicans ADE2 gene was ligated into plasmid pRC2312 and the construct transformed Ade^– strains of both C. albicans and S. cerevisiae to Ade⁺. The vector pRC2312 was also used to clone a fragment of C. albicans genomic DNA containing an aspartic proteinase gene. C. albicans transformants harboring this plasmid showed a two-fold increase in aspartic proteinase activity. However S. cerevisiae transformants showed no such increase in proteinase activity, suggesting the gene was not expressed in S. cerevisiae.     

Growth and energy production in Bacteroides amylophilus

The molar growth yield (Y _m) of Bacteroides amylophilus strain WP91 on maltose was 68±2 g/mol when determined from batch cultures at the peaks of maximal growth. Continued incubation led to considerable cell lysis. When calculated from batch cultures in exponential phase (specific growth rate, =0.57 h^-1) Y _m was 101 g/mol. The maximum value of Y _m in maltose-limited chemostat cultures at the maximum dilution rate (D) attainable (D==0.39 h^-1) was about 79 g/mol. Ammonia-Fmited chemostat cultures metabolized maltose with a much reduced efficiency and this was associated with a difference in morphology and chemical composition of the cells. The theoretical maximum molar growth yields (Y _m ^max ) were 55 and 114 g/mol for ammonia- and maltose-limited growth respectively. However, if account was taken of extracellular nitrogen-containing material in ammonia-limited cultures, Y _m ^max became 60. The maintenance coefficient (m _s), estimated from the lines relating the specific rate of maltose consumption (q _m) and D (where m _s=q _m at D=0), was 7.4±0.6×10^-4 mol maltose/g x h for both nutrient limitations. A difference in maintenance energy demand, independent of growth-rate, could not account, therefore, for the observed differences in Y _m between ammonia- and maltose-limited growth.     

MRI image-based FE modelling of the pelvis system and bladder filling

In this study, high-resolution magnetic resonance imaging was performed in the transaxial, coronal and sagittal planes to provide comprehensive structural details of the bladder and surrounding systems. Detailed finite-element (FE) models that were specific to each participant were developed by rendering the images, and the process of bladder filling was simulated. The overall model of bladder deformation was compared with repeated images of the filled bladder that were obtained using computed tomography to validate the FE models. The relationship between the changes in the key dimensions of the bladder and the increase in bladder volume during the filling process was also investigated. The numerical results showed that the bladder dimensions increased linearly with its volume during the filling process and the predicted coefficients are comparable to some of the published clinical results.     

Hepatitis C Transmission and Treatment in Contact Networks of People Who Inject Drugs

Hepatitis C virus (HCV) chronically infects over 180 million people worldwide, with over 350,000 estimated deaths attributed yearly to HCV-related liver diseases. It disproportionally affects people who inject drugs (PWID). Currently there is no preventative vaccine and interventions feature long treatment durations with severe side-effects. Upcoming treatments will improve this situation, making possible large-scale treatment interventions. How these strategies should target HCV-infected PWID remains an important unanswered question. Previous models of HCV have lacked empirically grounded contact models of PWID. Here we report results on HCV transmission and treatment using simulated contact networks generated from an empirically grounded network model using recently developed statistical approaches in social network analysis. Our HCV transmission model is a detailed, stochastic, individual-based model including spontaneously clearing nodes. On transmission we investigate the role of number of contacts and injecting frequency on time to primary infection and the role of spontaneously clearing nodes on incidence rates. On treatment we investigate the effect of nine network-based treatment strategies on chronic prevalence and incidence rates of primary infection and re-infection. Both numbers of contacts and injecting frequency play key roles in reducing time to primary infection. The change from “less-” to “more-frequent” injector is roughly similar to having one additional network contact. Nodes that spontaneously clear their HCV infection have a local effect on infection risk and the total number of such nodes (but not their locations) has a network wide effect on the incidence of both primary and re-infection with HCV. Re-infection plays a large role in the effectiveness of treatment interventions. Strategies that choose PWID and treat all their contacts (analogous to ring vaccination) are most effective in reducing the incidence rates of re-infection and combined infection. A strategy targeting infected PWID with the most contacts (analogous to targeted vaccination) is the least effective.     

The AgI/II Family Adhesin AspA Is Required for Respiratory Infection by Streptococcus pyogenes

Streptococcus pyogenes (GAS) is a human pathogen that causes pharyngitis and invasive diseases such as toxic shock syndrome and sepsis. The upper respiratory tract is the primary reservoir from which GAS can infect new hosts and cause disease. The factors involved in colonisation are incompletely known however. Previous evidence in oral streptococci has shown that the AgI/II family proteins are involved. We hypothesized that the AspA member of this family might be involved in GAS colonization. We describe a novel mouse model of GAS colonization of the nasopharynx and lower respiratory tract to elucidate these interactions. We used two clinical M serotypes expressing AspA, and their aspA gene deletant isogenic mutants in experiments using adherence assays to respiratory epithelium, macrophage phagocytosis and neutrophil killing assays and in vivo models of respiratory tract colonisation and infection. We demonstrated the requirement for AspA in colonization of the respiratory tract. AspA mutants were cleared from the respiratory tract and were deficient in adherence to epithelial cells, and susceptible to phagocytosis. Expression of AspA in the surrogate host Lactococcus lactis protected bacteria from phagocytosis. Our results suggest that AspA has an essential role in respiratory infection, and may function as a novel anti-phagocytic factor.     

Acquisition and voxelwise analysis of multi-subject diffusion data with tract-based spatial statistics

There is much interest in using magnetic resonance diffusion imaging to provide information on anatomical connectivity in the brain by measuring the diffusion of water in white matter tracts. Among the measures, the most commonly derived from diffusion data is fractional anisotropy (FA), which quantifies local tract directionality and integrity. Many multi-subject imaging studies are using FA images to localize brain changes related to development, degeneration and disease. In a recent paper, we presented a new approach, tract-based spatial statistics (TBSS), which aims to solve crucial issues of cross-subject data alignment, allowing localized cross-subject statistical analysis. This works by transforming the data from the centers of the tracts that are consistent across a study's subjects into a common space. In this protocol, we describe the MRI data acquisition and analysis protocols required for TBSS studies of localized change in brain connectivity across multiple subjects.